Quantum memories

Picture of a 2mm thick quantum memory crystal with a 250 nm wedge.

The distribution of quantum state/information over long distance is essential for quantum communications and quantum networks. However, the direct distribution across long distances is limited due to the losses in the quantum channels where the quantum states are being transmitted. An alternative to the direct distribution is to use quantum repeaters for long distance quantum network and quantum memories are the key components of quantum repeaters.

The quantum information group in Lund is using rare earth crystals aiming to realise multimode, long time, on demand quantum memories. The general approach is that a quantum state coded into light is absorbed and stored and the quantum state of the storage medium is controlled such that the absorption process is effectively time reversed, and the stored quantum state is emitted into the original mode. LLC researchers have demonstrated the first cavity enhanced quantum memory for these systems and achieved a memory efficiency of 56% and we believe there is room for further improvement.